The railway track bed, a ballast layer set above the road base and below the rail and sleeper, is a base of a railway frame. The railway track bed is used to support the rail and sleeper, equally distribute the heavy train load from the rail and sleepers onto the road base, reduce the distortion of the road base, and guarantee the safety of the transportation. Further, the ballasts possess a function of impact reduction and shock absorption. The ballast railway track bed possesses a wide range of application, because of its universal use and low construction cost.
The maintenance cost of the ballast railway track bed is very high. Apart from the regular maintenance, it is necessary to maintain the railway track bed in downtime by using of big maintenance equipments. During the service time, the position of the ballasts in the track bed structure is changed, due to the vibration from the rail and sleeper. Furthermore, the sharp edge of the ballast is gradually rubbed, and then becomes powder.
In addition, due to the ballast space structure, it is hard to avoid the coal, dust, sand and waste in the external environment enter into the ballast track bed to cause compaction. Even worse, the sleeper or rail might be broken, if the ballast track bed sink or liquidize to slurry.
In the prior art, there are many methods being used to reinforce ballast track bed by using of polymer material. For example, US2007172590 discloses a method for preparing a ballast track bed, wherein the ballast track bed comprises ballast stones and polyurethane foam, the polyurethane foam is obtained by the reaction between polyisocyanate and isocyanate-reactive compound. In addition, DE2305536A discloses a method to reinforce ballast track bed by pouring a polyurethane foaming material into the ballast space, foaming and curing.
However, the polyols used in the previous methods are limited to polyether polyol, because polyurethane foam based on polyester polyol is easy to hydrolysis, the mechanical properties reduce significantly after hydrolysis, therefore, the maintenance cycle of the ballast track bed is reduced significantly to avoid severe safety issues with regard to railway transportation.